Knowing the amounts of oil and water in the produced fluid outflow from hydrocarbon wells is of great commercial importance in today's petroleum industry. Problems arise in that crude oil contains many impurities such as gas in solution and paraffin, can be a very thick molasses-like material, contains sand and water, and presents many other obstacles to accurate testing of the oil and water contents. Errors in the range of 10% to even as high as 200% in determining the amount of oil in well production fluid or crude oil have been known to occur using conventional testing equipment and methods.
Because of the nature of crude oil and all of the impurities therein, it is not always possible to use ordinary orifice meters, turbine meters and the like. Conventional systems involve heating of the crude oil to dissolve any paraffin, since paraffin deposits will be detrimental to the equipment. Further, the heating aids in releasing dissolved gases which can produce inaccuracies in the results. Thereafter, the heated and thus degassed oil is separated and the water, sand and other foreign materials are removed. The oil remaining is passed on through conventional meters to measure the quantity of oil A gravity type separation, usually involving a weir, performs the actual oil/water separation.
Most crude oils contain both dissolved and free gas. The presence of this gas above certain percentages is a problem in producing accurate data according to the invention. It is for this reason necessary that, before the well fluids are measured for density and for mass, the free gas be removed. In the odd situation where a well produces fluids having no free gas, it is in that case possible to pass the produced well fluid directly into the invention apparatus.
Crude oil is produced together with varying amounts of water, and, in fact, the water can vary from zero to 99% of the total outflow of the well. This water can be in the form of free water or can be in the form of an emulsion together with the hydrocarbons. Still further, the emulsion can contain the water rather loosely combined with the hydrocarbon materials or rather intimately combined. In fact, it is possible that the combination of the water and crude oil can be so "tightly" emulsified that it is extremely difficult to separate the emulsion.
The prior art utilizes a system dependent upon a complex "plumbing" arrangement wherein a group of wells feed into a common production tank battery. The complex piping arrangement permits any one well feeding this battery to be in effect segregated out and have its output fed to a testing means. Tight emulsions in particular are a problem for conventional well testing. Further, in certain situations, exceedingly expensive equipment including heaters and the like are needed in order to adequately test all of the wells feeding into the common battery. The presence of paraffin in the hydrocarbon outflow creates additional problems, fouling of valves and meters, difficulty of measuring oil content, and the like.
Yet another problem resides in the presence of dissolved (solution) gas in the crude outflow from the well. This solution gas can evolve from the crude at any time during the process, and this random factor has a severe detrimental effect on the accuracy of conventional systems. A pressure drop anywhere in the conventional technique will, of course, cause an evolution of the gas.
Dependent upon the particular well and the crude oil and gas it produces, separation sometimes requires three phase and sometimes two phase separation. The invention can operate with both.
The invention also permits downsizing of the equipment used which is an advantage in producing a portable device, i.e., an apparatus embodying the invention which can be mounted on a simple pick-up truck to be brought out to the wellhead and used directly at the well. This portability occurs because it is often relatively easy to separate gas from well fluids, but relatively more time consuming to break apart the well fluids into the different components. Since the invention can work on gas free liquid whatever liquid components are contained therein, this permits the downsizing and the advantage of portability.
The term "free gas" as used herein shall be understood to mean any substance which is or will be in a gaseous state at the time it passes through the invention apparatus.
Knowing the amounts of oil and water in the produced fluid outflow from hydrocarbon wells is of great commercial importance in today's petroleum industry. In the conventional capacitance probe method of measurement, the accuracy of measurement for the amounts of oil and water deteriorates as the amount of water increases, especially at water contents above the 25-30% range. The use of ordinary orifice meters, turbine meters and the like is not desired because the meters, per se, are not too accurate and because the meters, especially the turbine meters, tend to require a lot of maintenance.
Usually, production well fluids are free of solids such as sand and have a pour point which is below the temperature at which the amounts of the oil and water are being measured. If solids are present, such as sand, then means must be provided to remove the sand before measurements are made to determine the oil and water content of the fluids. This is true for prior art devices and is also true for the use of the apparatus of this invention in order to obtain an accurate density signal. Further, high pour point crudes tend to plate paraffin out on any measuring device and this impairs the accuracy and efficiency of such devices. Conventional systems involve heating of the crude oil to a temperature above its pour point to prevent the deposition of paraffins in the measuring apparatus. Such a heating step would also be required using the method and apparatus of this invention in order to obtain an accurate density signal.
The prior art includes methods and apparatus that pass the sample mixture through a flow meter and an indirect density measuring device in series. This data can be processed to produce water and oil readings in volume units. However, the results are less accurate than those produced by the invention. The primary differences which are thought to produce these advantages include that the invention uses a mass measuring device in place of a flow meter, and that the same element (a vibrating tube) is used in the invention to measure mass and density, as compared to two separate means to do so in each prior art devices.
The prior art includes many devices which unsuccessfully attempt to solve the problems solved by the present invention. The ITT Barton Model 1200 device is said to determine the percentage of oil and water in a two-component fluid under flowing line conditions. The computer displays total oil and total water on two separate totalizers, plus total fluid flow rate indication. The percentages of oil and water are determined by measuring the flowing specific gravity of the fluid using a specially designed "ratio tube" and associated electronics. Liquid flow rate is measured using a turbine meter or positive displacement meter.
Testing has shown that the results using the ITT Barton device are not as accurate as the results using the device of this invention.
The present invention solves all of the above problems, and provides a measuring device which produces very highly accurate results.